Concise synthesis of a hexasaccharide present in the cell wall lipopolysaccharide of Azospirillum lipoferum Sp59b

Article abstract of DOI:10.1016/j.tetasy.2010.03.042

Concise chemical synthesis of a hexasaccharide repeating unit found in the cell wall lipopolysaccharide of Azospirillum lipoferum Sp59b was achieved in excellent yield. A [3+3] block synthetic strategy has been applied for the construction of the target hexasaccharide. During the synthesis, the orthogonal property of thioglycosides has been successfully exploited. Yields were high in all intermediate steps.

Full text of DOI:10.1016/j.tetasy.2010.03.042

Tetrahedron: Asymmetry 21 (2010) 725–730
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Concise synthesis of a hexasaccharide present in the cell wall
lipopolysaccharide of Azospirillum lipoferum Sp59b
*
Samir Ghosh, Anup Kumar Misra
Bose Institute, Division of Molecular Medicine, P-1/12, C.I.T. Scheme VII-M, Kolkata 700 054, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Concise chemical synthesis of a hexasaccharide repeating unit found in the cell wall lipopolysaccharide of
Azospirillum lipoferum Sp59b was achieved in excellent yield. A [3+3] block synthetic strategy has been
applied for the construction of the target hexasaccharide. During the synthesis, the orthogonal property
of thioglycosides has been successfully exploited. Yields were high in all intermediate steps.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 22 March 2010
Accepted 31 March 2010
Available online 3 May 2010
1. Introduction
experiments with this particular hexasaccharide. For this purpose,
sufficient quantities of the hexasaccharide repeating unit are re-
Among several growth-promoting rhizobacteria, Azospirilla play
a significant role in plant growth and development by fixing
atmospheric nitrogen and making it available to the plants in an
asymbiotic manner.1 Azospirilla are Gram-negative proteobacteria
widely present in soil and enhance the growth and yield of many
important crops through the production of several phytohormones,
vitamins and bioactive substances.2 They establish conjugate rela-
tionships with the roots of leguminous and non-leguminous crops.3
Spores of Azospirillum species are commonly used as biofertilizer.
Several macromolecules such as exopolysaccharides (EPS), lipo-
polysaccharides (LPS) and capsular polysaccharides (CPS) present
in the cell wall of Azospirillum have significant roles in establishing
the Azospirillum-plant interactions.4 As LPS is the major antigen
present in the bacterial outer cell wall, the role of the LPS together
with other polysaccharides is considered to be essential for the
plant-bacterial interactions. Despite their usefulness only a few
structures of LPS have been reported from Azospirillum species.5
Fedonenko et al. reported the structure of a hexasaccharide repeat-
ing unit found in the LPS of Azospirillum lipoferum Sp59b (Fig. 1).6
Development of plant growth-promoting agents for the
enhancement of crop production is currently a major thrust. For
a detailed understanding of the role of the LPS in the plant-bacte-
rial interactions it is essential to carry out different biological
quired, which is not possible from the natural source. A concise
chemical synthetic strategy could provide the required quantity
of the hexasaccharide repeating unit as well as its analogues. As
a part of our ongoing program on the synthesis of complex oligo-
saccharides,7 we report herein a concise chemical synthesis of
the hexasaccharide as its 4-methoxyphenyl glycoside found in
the cell wall lipopolysaccharide of A. lipoferum Sp59b (Fig. 2). The
4-methoxyphenyl group has been chosen as a temporary protect-
ing group at the reducing end due to its easy removal under oxida-
tive conditions to furnish a hexasaccharide hemiacetal derivative
to prepare glycoconjugate derivatives.
2. Results and discussion
In order to achieve the synthesis of the target hexasaccharide as
its 4-methoxyphenyl glycoside (Fig. 2) containing a b-
unit linked to a terminal tri- -rhamnoside moiety 1, a [3+3] block
synthetic strategy has been undertaken. Due to the difficulty in
the preparation of the b- -mannopyranosidic linkage directly from
-mannosyl derivatives, a suitably protected b- -Glucose deriva-
tive has been used as the precursor of b- -mannose moiety. A num-
ber of noteworthy features are present in the synthetic strategy,
which are (a) conversion of the b- -glucose unit to the b- -man-
D-mannose
L
D
D
D
D
D
D
α-L-Rhap-(1→3)-α-L-Rhap-(1→2)-α-L-Rhap-(1→3)-β-D-Manp
1
↓
4
→3)-α-D-Galp-(1→3)-β-D-Galp-(1→
Figure 1. Hexasaccharide repeating unit of the lipopolysaccharide found in the cell wall of Azospirillum lipoferum Sp59b.
* Corresponding author. Tel.: +91 33 25693240; fax: +91 33 2355 3886.
E-mail address: akmisra69@gmail.com (A.K. Misra).
0957-4166/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2010.03.042

726
S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 725–730
OH
O
2 + 3
HO
HO
O
HO
D O
O
Ph
C
a
O
OH
HO
HO
E O
HO
HO
HO
O
O
HO
O
F O
OH
B
HO
O
O
O
BnO
B
OBn
O
HO
BnO
A
HO
O
OMp
1
BnO
A
OH
O
OMp
OBn
Mp: 4-Methoxyphenyl
4
b
Ph
O
OBn
HO
BnO
HO
OBn
O
O
O
Ph
O
AcO
B
BnO
OBn
O
OMp
OBn
O
BnO
O
O
OMp
SEt
BnO
SEt
BnO
A
OBn
O
OAc
OBn
6
2
3
5
OMp
SEt
OC(NH)CCl3
a
6
Ph
O
O
O
O
O
BnO
BnO
O
BnO
AcO
AcO
C
OBn
O
O
RO
HO
OH
OAc
OAc
OR
BnO
12
10
B
9
BnO OBn
O
BnO
A
O
OMp
7:
8:
Figure 2. Structure of the synthesized hexasaccharide as its 4-methoxyphenyl
glycoside corresponding to the lipopolysaccharide of Azospirillum lipoferum Sp59b.
R = Ac
R = H
OBn
c
Scheme 1. Reagents and conditions: (a) N-iodosuccinimide (NIS), TfOH, CH2Cl2, MS
4 Å, ꢀ40 °C, 30 min, 80% for 4 and 81% for 7; (b) Et3SiH, I2, CH2Cl2, 0–5 °C, 15 min,
75%; (c) CH3ONa, CH3OH, room temperature, 3 h, quantitative.
nose unit after completion of the glycosylation steps, (b) prepara-
tion of two trisaccharide derivatives as their 4-methoxyphenyl
(OMp) glycosides 8 and 13 and conversion of one OMp glycoside
13 to trichloroacetimidate derivative 14 for its use as glycosyl
donor, (c) exclusively regio- and stereoselective glycosylation of
The presence of signals at d 5.07 (br s, H-1E), 4.92 (br s, H-1F) in
the 1H NMR and d 99.6 (C-1F), 82.4 (C-1E) in the 13C NMR spectra
confirmed its formation. In this case thioglycoside derivative 10
acts as an orthogonal glycosyl acceptor. Further glycosylation of
the disaccharide derivative 11 with compound 1216 in the presence
of NIS-TfOH furnished trisaccharide derivative 13 in 78% yield,
which was confirmed from its NMR spectral analysis [signals at d
5.34 (br s, H-1D), 5.05 (br s, H-1E), 4.97 (br s, H-1F) in the 1H
NMR and at d 99.6 (C-1E), 99.5 (C-1F), 97.9 (C-1D) in the 13C NMR
spectra confirmed the structure of 13]. Removal of the anomeric
4-methoxyphenyl group of trisaccharide derivative 13 using
ammonium cerium nitrate (CAN)17 followed by treatment of the
hemiacetal derivative with trichloroacetonitrile in the presence
of DBU15a resulted in the formation of trisaccharide trichloroace-
timidate derivative 14 in 77% yield (Scheme 2).
an
a trisaccharide acceptor 8 having 2,3-dihydroxylated
moiety under Schmidt glycosylation condition and (d) use of a
-rhamnosyl thioglycoside derivative 10 as a glycosyl acceptor in
the presence of -rhamnosyl trichloroacetimidate derivative 9 as
L
-rhamnosyl trisaccharide trichloroacetimidate donor 14 using
D-glucose
L
L
the glycosyl acceptor.
A dihydroxyl groups containing trisaccharide acceptor 8 has
been synthesized from three suitably derivatized monosaccharide
intermediates 2,8 39 and 6.10 Stereoselective 1,2-cis glycosylation
of D-galactose-derived compound 2 with the D-galactosyl thiogly-
coside derivative 3 in the presence of N-iodosuccinimide (NIS)
and trifluoromethanesulfonic acid (TfOH)11 furnished disaccharide
derivative 4 in 80% yield. Exclusive formation of the 1,2-cis glycosyl
linkage was achieved using a glycosyl donor having a non-partici-
pating benzyloxy group at the C-2 position of the glycosyl donor 3
which was confirmed from its NMR spectral data [d 5.21 (d,
J = 3.3 Hz, H-1B), 4.86 (d, J = 7.6 Hz, H-1A) in the 1H NMR and at d
103.8 (C-1A), 101.3 (PhCH), 96.4 (C-1B) in the 13C NMR spectra].
Regioselective ring opening of the benzylidene acetal of compound
4 using a combination of triethylsilane and molecular iodine12 pro-
duced disaccharide acceptor 5 in 75% yield. Stereoselective 1,2-
trans glycosylation of compound 5 with thioglycoside derivative
6 in the presence of NIS-TfOH11 afforded the trisaccharide deriva-
tive 7 in 81% yield, which on saponification quantitatively fur-
nished trisaccharide diol acceptor 8. Exclusive formation of the
1,2-trans glycosylation product 7 was achieved due to the presence
of participating acetoxy group at the C-2 position of glycosyl donor
6, which was further confirmed from the spectral analysis of com-
pound 7 [d 5.20 (br s, H-1B), 4.74 (d, J = 7.9 Hz, H-1A), 4.71 (d,
J = 9.8 Hz, H-1C) in 1H NMR and d 103.6 (C-1C), 102.5 (C-1A),
101.9 (PhCH), 95.7 (C-1B) in the 13C NMR] (Scheme 1).
SEt
E
O
BnO
a
9 + 10
O
OAc
F
O
AcO
AcO
OAc
11
12
b
OR
D
O
BnO
BnO
O
E
O
BnO
O
OAc
F
O
AcO
AcO
OAc
In another experiment, a di-
derivative 11 was synthesized in 83% yield by stereoselective
condensation of
-rhamnosyl trichloroacetimidate donor 913 and
-rhamnosyl thioglycoside derivative 1014 as acceptor in the pres-
L-rhamnopyranosyl thioglycoside
13: R = Mp
c, d
14:
R = C(NH)CCl3
L
L
Scheme 2. Reagents and conditions: (a) TMSOTf, CH2Cl2, ꢀ20 °C, 45 min, 83%; (b)
NIS, TfOH, CH2Cl2, MS 4 Å, ꢀ40 °C, 30 min, 78%; (c) CAN, CH3CN–H2O (9:1), 0–5 °C,
2 h; (d) CCl3CN, DBU, CH2Cl2, ꢀ10 °C, 1 h, 77% in two steps.
ence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) as
glycosylation activator under Schmidt’s glycosylation condition.15

S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 725–730
727
Regioselective coupling of the trisaccharide donor 14 with the
trisaccharide diol acceptor 8 in the presence of TMSOTf15 resulted
in the stereoselective formation of the hexasaccharide derivative
15 in 76% yield. Compound 15 was characterized by the presence
of signals at d 5.24 (br s, H-1E), 5.19 (d, J = 3.1 Hz, H-1B), 5.00 (br
s, H-1F), 4.97 (br s, H-1D), 4.76 (d, J = 7.4 Hz, H-1A), 4.31 (d,
J = 7.8 Hz, H-1C) in the 1H NMR and at d 106.5 (C-1C), 103.6 (C-1A),
101.9 (PhCH), 99.5 (3C, C-1D, C-1E, C-1F), 96.1 (C-1B) in the 13C
NMR spectra. Exclusive formation of the (1?3)-glycosylation prod-
uct was confirmed from the 1D and 2D NMR spectra analysis of the
acetylated product of compound 15 (data not included). Oxidation
of the free hydroxyl group at C-2C position in compound 15 using
Dess–Martin periodinane18 followed by sodium borohydride reduc-
tion19 of the resulting ketone afforded the hexasaccharide deriva-
b-
D
-glucosyl moiety into b-
D
-mannosyl moiety in the later stage
avoided the difficulties for the formation of b-D-mannosyl linkage.
All intermediate steps were high yielding and highly reproducible
for a scale-up preparation.
4. Experimental
4.1. General methods
All the reactions were monitored by thin layer chromatography
over silica gel-coated TLC plates. The spots on TLC were visualized
by warming ceric sulfate (2% Ce(SO4)2 in 2 N H2SO4)-sprayed plates
in hot plate. Silica gel 230–400 mesh was used for column chroma-
tography. 1H and 13C NMR, 2D COSY, HSQC and NOESY spectra
were recorded on a Brucker Advance DPX 300 MHz using CDCl3
and D2O as solvents and TMS as internal reference unless stated
otherwise. Chemical shift values are expressed in d ppm. ESI-MS
were recorded on a Micromass Quttro II mass spectrometer. Ele-
mentary analysis was carried out on a Carlo Erba-1108 analyzer.
Optical rotations were measured at 25 °C on a Perkin Elmer 341
polarimeter. Commercially available grades of organic solvents of
adequate purity are used in many reactions.
tive containing a b-D-mannosidic moiety. Due to the removal of
O-acetyl groups present in compound 15 under sodium borohy-
dride reduction conditions, the resulting epimerized hexasaccha-
ride derivative was acetylated to give compound 16 in 74% yield
and characterized by NMR spectroscopic analysis. Appearance of
signals at d 5.47 (d, J = 2.6 Hz, H-2C), 5.06 (d, J = 2.9 Hz, H-1B), 4.99
(br s, H-1F), 4.97 (br s, H-1E), 4.77 (br s, H-1D), 4.74 (br s, H-1C),
4.66 (d, J = 7.7 Hz, H-1A) in the 1H NMR and d 103.7 (C-1A), 101.6
(PhCH), 100.0 (C-1C), 99.5 (C-1F), 99.0 (C-1E), 95.9 (C-1D), 95.6 (C-
1B) in the 13C NMR spectra confirmed the formation of compound
16. Finally, complete deprotection of the hexasaccharide derivative
under saponification followed by hydrogenolysis over Pd(OH)2–C20
furnished the target hexasaccharide 1 as its 4-methoxyphenyl gly-
coside in 71% yield. Signals at d 4.99 (br s, H-1E), 4.97 (d, J = 3.7 Hz,
H-1B), 4.95 (br s, H-1D), 4.85 (br s, H-1F), 4.71 (d, J = 7.9 Hz, H-1A),
4.69 (br s, H-1A) in the 1H NMR and at d 103.1 (C-1F), 102.9 (C-1E),
102.8 (C-1C), 101.5 (C-1A), 97.0 (C-1B), 95.4 (C-1D) in the 13C NMR
spectra confirmed the structure of compound 1 (Scheme 3).
4.1.1. 4-Methoxyphenyl (2,3-di-O-benzyl-4,6-O-benzylidene-
-galactopyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b- -galacto-
pyranoside 4
a-
D
D
To a solution of compound 2 (1.5 g, 2.58 mmol) and compound 3
(1.5 g, 3.05 mmol) in anhydrous CH2Cl2 (15 mL) was added MS 4 Å
(2 g) and the reaction mixture was allowed to stir at room temper-
ature for 30 min under argon. The reaction mixture was cooled to
ꢀ40 °C and N-iodosuccinimide (NIS; 825 mg, 3.66 mmol) followed
by TfOH (8
l
L) were added to it. After stirring at the same temper-
L), fil-
ature for 30 min the reaction was quenched with Et3N (50
l
tered through a CeliteÒ bed and washed with CH2Cl2 (50 mL). The
combined organic layer was washed with 5% Na2S2O3, satd NaHCO3,
water in succession, dried (Na2SO4) and concentrated under re-
duced pressure. The crude product was purified over SiO2 using
hexane–EtOAc (8:1) as an eluant to give pure 4 (2.1 g, 80%). Colour-
8 + 14
a
Ph
D O
O
BnO
O
O
C
less oil; ½a 2D5
ꢁ
¼ þ5:4 (c 1.0, CHCl3); IR (neat): 3062, 3032, 2920,
O
O
OBn
O
BnO
BnO
OH
BnO
E
AcO
AcO
AcO
B
BnO
2902, 2854, 1605, 1508, 1453, 1402, 1366, 1249, 1154, 1102,
O
OBn
O
O
F O
1079, 1027, 994, 825, 797, 696 cmꢀ1 1H NMR (500 MHz, CDCl3):
;
O
AcO
BnO
O
A
OMp
15
d 7.48–7.12 (m, 30H, Ar-H), 7.00 (d, J = 9.1 Hz, 2H, Ar-H), 6.78 (d,
J = 9.1 Hz, 2H, Ar-H), 5.27 (s, 1H, PhCH), 5.21 (d, J = 3.3 Hz, 1H, H-
1B), 5.09 (d, J = 11.6 Hz, 1H, PhCH2a), 5.06 (d, J = 10.6 Hz, 1H,
PhCH2a), 4.90 (d, J = 11.6 Hz, 1H, PhCH2b), 4.86 (d, J = 7.6 Hz, 1H,
H-1A), 4.78 (d, J = 12.2 Hz, 1H, PhCH2a), 4.73 (d, J = 12.2 Hz, 1H,
PhCH2b), 4.70 (d, J = 11.4 Hz, 1H, PhCH2a), 4.51 (d, J = 10.6 Hz, 1H,
PhCH2b), 4.45 (d, J = 11.7 Hz, 1H, PhCH2a), 4.40 (d, J = 11.4 Hz, 1H,
PhCH2b), 4.38 (d, J = 11.7 Hz, 1H, PhCH2b), 4.18–4.15 (dd, J = 10.1,
3.3 Hz, 1H, H-3A), 4.05–4.01 (m, 2H, H-2A, H-3B), 3.91 (d,
J = 2.4 Hz, 1H, H-4B), 3.86–3.80 (m, 3H, H-2B, H-5B, H-6aB), 3.78 (d,
J = 3.2 Hz, 1H, H-4A), 3.75 (s, 3H, OCH3), 3.65–3.56 (m, 3H, H-5A,
H-6abA), 3.27–3.24 (m, 1H, H-6bB); 13C NMR (125 MHz, CDCl3): d
155.6–114.9 (Ar-C), 103.8 (C-1A), 101.3 (PhCH), 96.4 (C-1B), 78.6
(C-2A), 77.9 (C-3B), 76.5 (C-2B), 75.9 (C-3A), 75.8 (PhCH2), 75.2
(PhCH2), 75.0 (PhCH2), 74.8 (C-5A), 74.2 (C-4A), 73.9 (PhCH2), 72.9
(C-4B), 72.1 (PhCH2), 69.5 (C-6A), 69.3 (C-6B), 62.8 (C-5B), 56.1
(OCH3); ESI-MS: m/z 1033.4 [M+Na]+; Anal. Calcd for C55H62O18
(1010.39): C, 65.34; H, 6.18. Found: C, 65.15; H, 6.40.
OBn
b, c, d
OAc
O
Ph
D O
O
BnO
O
C
O
O
OBn
O
BnO
BnO
AcO
AcO
AcO
BnO
B
O
F O
OBn
O
O
BnO
O
BnO
A
O
AcO
16
e, f
OMp
OBn
1
Scheme 3. Reagents and conditions: (a) TMSOTf, CH2Cl2, ꢀ20 °C, 45 min, 76%; (b)
Dess–Martin periodinane, CH2Cl2, room temperature, 2 h; (c) NaBH4, CH3OH, 0 °C–
room temperature, 12 h; (d) acetic anhydride, pyridine, room temperature, 5 h, 74%
in three steps; (e) CH3ONa, CH3OH, room temperature, 3 h; (f) H2, 20% Pd(OH)2–C,
CH3OH, room temperature, 24 h, 71%.
3. Conclusion
4.1.2. 4-Methoxyphenyl (2,3,6-tri-O-benzyl-
pyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b- -galactopyranoside 5
To a solution of compound 4 (2.0 g, 1.98 mmol) in CH2Cl2
(10 mL) were added Et3SiH (650 L, 4.07 mmol) and iodine
(150 mg, 0.59 mmol) at 0 °C. After stirring at the same temperature
a-D-galacto-
In summary, a concise synthetic strategy for the preparation of
the hexasaccharide repeating unit of the lipopolysaccharide found
in the cell wall of A. lipoferum Sp59b has been developed. Regio-
and stereoselective [3+3] glycosylation allowed achieving the tar-
get hexasaccharide in minimum number of steps. Conversion of a
D
l

728
S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 725–730
for 15 min the reaction mixture was diluted with CH2Cl2 (50 mL)
and successively washed with 5% Na2S2O3, satd NaHCO3 and water.
The organic layer was dried over Na2SO4 and concentrated under
reduced pressure. The crude product was purified over SiO2 using
hexane–EtOAc (6:1) as an eluant to give pure 5 (1.5 g, 75%). Colour-
4.1.4. 4-Methoxyphenyl (4,6-O-benzylidene-b-
-(1?4)-(2,3,6-tri-O-benzyl- -galactopyranosyl)-(1?3)-2,4,6-
tri-O-benzyl-b- -galactopyranoside 8
D-glucopyranosyl)
a-D
D
A solution of compound 7 (1.4 g, 1.04 mmol) in 0.1 M CH3ONa
in methanol (30 mL) was allowed to stir at room temperature for
3 h. The reaction mixture was neutralized with Dowex 50W X8
(H+) resin, filtered and concentrated under reduced pressure. The
crude product was passed through a short pad of SiO2 to give pure
less oil; ½a 2D5
¼ þ3:6 (c 1.0, CHCl3); IR (neat): 3462, 3062, 3030,
ꢁ
2919, 2852, 1725, 1606, 1506, 1454, 1363, 1221, 1098, 1028,
909, 827, 749, 734, 696 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.38–
;
7.15 (m, 30H, Ar-H), 6.98 (d, J = 8.9 Hz, 2H, Ar-H), 6.77 (d,
J = 8.9 Hz, 2H, Ar-H), 5.21 (d, J = 3.3 Hz, 1H, H-1B), 5.06 (d,
J = 11.5 Hz, 1H, PhCH2), 5.02 (d, J = 10.7 Hz, 1H, PhCH2), 4.85 (d,
J = 11.6 Hz, 1H, PhCH2), 4.78 (d, J = 7.6 Hz, 1H, H-1A), 4.72–4.68
(m, 2H, PhCH2), 4.64 (d, J = 11.2 Hz, 1H, PhCH2), 4.45–4.36 (m,
5H, PhCH2), 4.31 (d, J = 11.2 Hz, 1H, PhCH2), 4.25–4.23 (m, 1H, H-
5B), 4.07–4.03 (dd, J = 7.8, 7.8 Hz, 1H, H-2A), 4.02–3.99 (dd, J = 9.8,
3.2 Hz, 1H, H-2B), 3.93 (d, J = 2.3 Hz, 1H, H-4A), 3.89–3.87 (dd,
J = 9.8, 3.0 Hz, 1H, H-3B), 3.86–3.84 (dd, J = 10.0, 2.3 Hz, 1H, H-
3A), 3.77–3.76 (m, 1H, H-4B), 3.75 (s, 3H, OCH3), 3.61–3.56 (m,
3H, H-5A, H-6abA), 3.42–3.40 (m, 2H, H-6abB); 13C NMR (125 MHz,
CDCl3): d 154.1–114.9 (Ar-C), 103.8 (C-1A), 95.6 (C-1B), 78.5 (C-
2A), 78.2 (C-3B), 77.0 (C-3A), 76.1 (C-2B), 75.8 (PhCH2), 75.0 (PhCH2),
74.9 (PhCH2), 74.1 (C-5A), 73.9 (PhCH2), 73.5 (PhCH2), 72.8 (C-4A),
72.4 (PhCH2), 70.5 (C-6B), 69.3 (C-6A), 68.8 (C-4B), 68.3 (C-5B),
56.1 (OCH3); ESI-MS: m/z 1035.4 [M+Na]+; Anal. Calcd for
C55H64O18 (1012.40): C, 65.21; H, 6.37. Found: C, 65.0; H, 6.55.
8 (1.3 g, quantitative). Colourless oil; ½a D25
¼ þ2:6 (c 1.0, CHCl3); IR
ꢁ
(neat): 3431, 3030, 2922, 2854, 1507, 1454, 1369, 1221, 1099,
1074, 1028, 912, 750, 735, 697 cmꢀ1 1H NMR (500 MHz, CDCl3):
;
d 7.33–6.92 (m, 35H, Ar-H), 6.91 (d, J = 9.1 Hz, 2H, Ar-H) 6.73 (d,
J = 9.1 Hz, 2H, Ar-H), 5.47 (s, 1H, PhCH), 5.15 (d, J = 3.2 Hz, 1H, H-
1B), 5.03 (d, J = 11.3 Hz, 1H, PhCH2), 4.97 (d, J = 11.3 Hz, 1H, PhCH2),
4.77 (2 d, J = 12.2 Hz, 2H, PhCH2), 4.76 (d, J = 7.6 Hz, 1H, H-1A),
4.69–4.64 (m, 3H, PhCH2), 4.45–4.35 (m, 3H, PhCH2), 4.33 (d,
J = 7.7 Hz, 1H, H-1C), 4.30–4.26 (m, 2H, PhCH2), 4.24–4.22 (m, 1H,
H-5B), 4.09–4.06 (m, 1H, H-6aC), 4.07–4.00 (m, 2H, H-2A, H-2B),
3.96–3.94 (m, 1H, H-3B), 3.91 (d, J = 2.5 Hz, 1H, H-4B), 3.78–3.66
(m, 7H, H-3A, H-4A, H-5A, H-6abA, H-6aB, H-6bC), 3.58 (s, 3H,
OCH3), 3.52–3.40 (m, 4H, H-2C, H-3C, H-4C, H-6bB), 3.25–3.20 (m,
1H, H-5C); 13C NMR (125 MHz, CDCl3): d 155.6–114.8 (Ar-C),
106.5 (C-1C), 103.5 (C-1A), 102.2 (PhCH) 95.9 (C-1B), 80.6 (C-3A),
80.4 (C-2B), 78.3 (C-2A), 78.2 (C-4C), 78.0 (C-4B), 76.9 (C-3B), 76.1
(C-5A), 75.6 (PhCH2), 75.0 (PhCH2), 74.9 (PhCH2), 74.4 (PhCH2),
73.9 (2C, C-2C, C-4A), 73.1 (C-3C), 73.0 (PhCH2), 69.1 (C-6B), 68.9
(C-6A), 68.7 (C-6C), 68.5 (C-5B), 67.1 (C-5C), 55.9 (OCH3); ESI-MS:
m/z 1285.5 [M+Na]+; Anal. Calcd for C68H78O23 (1262.49): C,
64.65; H, 6.22. Found: C, 64.48; H, 6.48.
4.1.3. 4-Methoxyphenyl (2,3-di-O-acetyl-4,6-O-benzylidene-b-
glucopyranosyl)-(1?4)-(2,3,6-tri-O-benzyl- -galacto-
pyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b- -galactopyranoside 7
D-
a-D
D
To a solution of compound 5 (1.4 g, 1.38 mmol) and com-
pound 6 (660 mg, 1.66 mmol) in anhydrous CH2Cl2 (15 mL) was
added MS 4 Å (2 g) and the reaction mixture was allowed to stir
at room temperature for 30 min under argon. The reaction mix-
ture was cooled to ꢀ40 °C and N-iodosuccinimide (NIS; 450 mg,
4.1.5. Ethyl 2,3,4-tri-O-acetyl-
a-L-rhamnopyranosyl-(1?3)-2-O-
acetyl-4-O-benzyl-1-thio- -rhamnopyranoside 11
a
-L
A solution of compound 9 (1.8 g, 4.14 mmol) and compound 10
(1.0 g, 2.94 mmol) in anhydrous CH2Cl2 (15 mL) was allowed to stir
at ꢀ20 °C for 15 min under argon. To the cold reaction mixture was
2.0 mmol) followed by TfOH (5 lL) were added to it. After stir-
ring at the same temperature for 30 min the reaction was
added TMSOTf (50 lL) and the reaction mixture was allowed to stir
quenched with Et3N (50
l
L), filtered through a CeliteÒ bed and
at same temperature for 45 min. The reaction was quenched with
washed with CH2Cl2 (50 mL). The organic layer was washed with
5% Na2S2O3, satd NaHCO3, water in succession, dried (Na2SO4)
and concentrated under reduced pressure. The crude product
was purified over SiO2 using hexane–EtOAc (6:1) as an eluant
Et3N (100 L) and diluted with CH2Cl2 (50 mL). The organic layer
l
was washed with satd NaHCO3 and water in succession, dried
(Na2SO4) and concentrated under reduced pressure. The crude
product was purified over SiO2 using hexane–EtOAc (7:1) as an elu-
to give pure 7 (1.5 g, 81%). Colourless oil; ½a D25
ꢁ
¼ þ2:2 (c 1.0,
ant to give pure 11 (1.5 g, 83%). Colourless oil; ½a D25
¼ ꢀ8:8 (c 1.0,
ꢁ
CHCl3); IR (neat): 3458, 3031, 2923, 2863, 1752, 1507, 1454,
CHCl3); IR (neat): 3476, 3033, 2962, 2926, 2854, 1749, 1627,
1498, 1456, 1375, 1260, 1226, 1138, 1040, 982, 933, 911, 803,
1370, 1242, 1219, 1097, 1067, 1029, 906, 750, 735, 697 cmꢀ1
;
1H NMR (500 MHz, CDCl3): d 7.37–7.18 (m, 35H, Ar-H), 6.94 (d,
J = 9.1 Hz, 2H, Ar-H) 6.75 (d, J = 9.1 Hz, 2H, Ar-H), 5.47 (s, 1H,
PhCH), 5.31 (t, J = 9.4 Hz each, 1H, H-3C), 5.20 (br s, 1H, H-1B),
5.03–4.99 (m, 2H, 2PhCH2), 4.98 (t, J = 10.0 Hz each, 1H, H-2C),
4.78–4.69 (m, 3H, 3PhCH2), 4.74 (d, J = 7.9 Hz, 1H, H-1A), 4.71
(d, J = 9.8 Hz, 1H, H-1C), 4.61–4.59 (m, 2H, PhCH2), 4.44–4.33
(m, 5H, PhCH2), 4.31–4.29 (m, 1H, H-5B), 4.15–4.12 (m, 1H, H-
6aC), 4.06–4.02 (dd, J = 7.9, 7.9 Hz, 1H, H-2A), 3.91–3.88 (m, 3H,
H-2B, H-3B, H-4A) 3.85–3.82 (dd, J = 2.5, 9.9 Hz, 1H, H-3A), 3.75–
3.74 (m, 1H, H-4B), 3.74 (s, 3H, OCH3), 3.68–3.64 (m, 1H, H-
6bC), 3.64 (t, J = 9.4 Hz each, 1H, H-4C), 3.58–3.50 (m, 4H, H-5A,
H-6abA, H-6aB), 3.42–3.35 (m, 2H, H-5C, H-6bB), 2.04, 1.83 (2 s,
749, 699 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.24–7.19 (m, 5H,
;
Ar-H), 5.22–5.21 (m, 1H, H-2F), 5.16–5.15 (m, 1H, H-2E), 5.14–
5.11 (dd, J = 10.0, 3.3 Hz, 1H, H-3F), 5.07 (br s, 1H, H-1E), 4.95 (t,
J = 9.9 Hz, 1H, H-4F), 4.92 (br s, 1H, H-1F), 4.71 (d, J = 10.9 Hz, 1H,
PhCH2), 4.58 (d, J = 10.9 Hz, 1H, PhCH2), 4.01–3.97 (m, 2H, H-3E,
H-5E), 3.82–3.79 (m, 1H, H-5F), 3.44 (t, J = 9.5 Hz, 1H, H-4E), 2.57–
2.51 (m, 2H, SCH2CH3), 2.15 (s, 3H, COCH3), 2.00 (s, 3H, COCH3),
1.99 (s, 3H, COCH3), 1.91 (s, 3H, COCH3), 1.26 (d, J = 6.3 Hz, 3H,
CCH3), 1.21 (t, J = 7.4 Hz, SCH2CH3), 1.13 (d, J = 6.3 Hz, 3H, CCH3);
13C NMR (125 MHz, CDCl3): d 170.7 (COCH3), 170.2 (2C; 2COCH3),
170.0 (COCH3), 138.2–128.1 (Ar-C), 99.6 (C-1F), 82.4 (C-1E), 81.3
(C-4E), 77.2 (C-3E), 75.9 (PhCH2), 74.2 (C-2E), 71.0 (C-4F), 70.1 (C-
2F), 69.4 (C-3F), 68.9 (C-5E), 67.7 (C-5F), 25.9 (SCH2CH3), 21.4
(COCH3), 21.2 (COCH3), 21.1 (COCH3), 21.0 (COCH3), 18.3 (SCH2CH3),
17.7 (CCH3), 15.4 (CCH3); ESI-MS: m/z 635.2 [M+Na]+; Anal. Calcd
for C29H40O12S (612.22): C, 56.85; H, 6.58. Found: C, 56.67; H, 6.80.
6H, 2COCH3); 13C NMR (125 MHz, CDCl3):
d 170.5 (COCH3),
170.2 (COCH3), 155.5–114.9 (Ar-C), 103.6 (C-1C), 102.5 (C-1A),
101.9 (PhCH), 95.7 (C-1B), 78.8 (C-4C), 78.6 (C-2B), 78.5 (C-2A),
77.7 (C-3A), 77.3 (C-3B), 76.7 (C-4B), 75.5 (PhCH2), 75.0 (PhCH2),
74.9 (PhCH2), 74.1 (C-5A), 73.8 (PhCH2), 73.5 (PhCH2), 73.0 (C-
4A), 72.9 (PhCH2), 72,9 (C-2C), 72.2 (C-3C), 69.9 (C-6B), 69.3 (C-
6A), 69.1 (C-5B), 68.9 (C-6C), 66.4 (C-5C), 56.1 (OCH3), 21.2
(COCH3), 21.1 (COCH3); ESI-MS: m/z 1369.5 [M+Na]+; Anal. Calcd
for C72H82O25 (1346.51): C, 64.18; H, 6.13. Found: C, 64.0; H,
6.35.
4.1.6. 4-Methoxyphenyl (2,3,4-tri-O-acetyl-
pyranosyl)-(1?3)-(2-O-acetyl-4-O-benzyl-
pyranosyl)-(1?2)-3,4-di-O-benzyl- -rhamnopyranoside 13
a-
L
-rhamno-
a-L-rhamno-
a-L
To a solution of compound 11 (1.5 g, 2.45 mmol) and compound
12 (1.0 g, 2.29 mmol) in anhydrous CH2Cl2 (15 mL) was added MS

S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 725–730
729
4 Å (2 g) and the reaction mixture was allowed to stir at room
temperature for 30 min under argon. The reaction mixture was
cooled to ꢀ40 °C and N-iodosuccinimide (NIS; 660 mg, 2.93 mmol)
2872, 1749, 1508, 1455, 1371, 1244, 1226, 1138, 1082, 1057,
1028, 912, 750, 698 cmꢀ1 1H NMR (500 MHz, CDCl3): d 7.32–7.21
;
(m, 50H, Ar-H), 6.94 (d, J = 9.1 Hz, 2H, Ar-H), 6.75 (d, J = 9.1 Hz,
2H, Ar-H), 5.46 (s, 1H, PhCH), 5.34–5.33 (m, 1H, H-2F), 5.32–5.31
(m, 1H, H-2E), 5.24 (br s, 1H, H-1E), 5.23–5.21 (m, 1H, H-3F), 5.19
(d, J = 3.1 Hz, 1H, H-1B), 5.00 (br s, 1H, H-1F), 5.04 (t, J = 9.4 Hz each,
1H, H-4F), 4.99 (d, J = 11.4 Hz, 1H, PhCH2), 4.97 (br s, 1H, H-1D), 4.95
(d, J = 11.3 Hz, 1H, PhCH2), 4.80 (d, J = 11.2 Hz, 1H, PhCH2), 4.76 (d,
J = 7.4 Hz, 1H, H-1A), 4.75–4.71 (m, 3H, PhCH2), 4.67–4.73 (m, 5H,
PhCH2), 4.57 (d, J = 10.9 Hz, 1H, PhCH2), 4.55 (d, J = 10.9 Hz, 1H,
PhCH2), 4.46–4.37 (m, 3H, PhCH2), 4.31 (d, J = 7.8 Hz, 1H, H-1C),
4.28 (d, J = 11.9 Hz, 1H, PhCH2), 4.25–4.18 (m, 3H, H-3C, H-3D,
PhCH2), 4.11–4.08 (m, 2H, H-2D, H-3E), 4.04–3.99 (m, 4H, H-2A, H-
2B, H-5E, H-6aC), 3.98–3.95 (m, 1H, H-3B), 3.91 (d, J = 2.5 Hz, 1H, H-
4B), 3.89–3.85 (m, 2H, H-3A, H-6bC), 3.81–3.76 (m, 2H, H-5D, H-5F),
3.75 (s, 3H, OCH3), 3.72 (br s, 1H, H-4A), 3.68 (t, J = 10.3 Hz, 1H, H-
4E), 3.60–3.56 (m, 4H, H-5A, H-5B, H-6abB), 3.47–3.41 (m, 4H, H-2C,
H-4C, H-6abA), 3.40–3.36 (t, J = 9.5 Hz, 1H, H-4D), 3.28–3.23 (m, 1H,
H-5C), 2.16 (s, 3H, COCH3), 2.07 (s, 3H, COCH3), 2.05 (s, 3H, COCH3),
1.97 (s, 3H, COCH3), 1.22 (d, J = 6.2 Hz, 3H, CCH3), 1.17 (d, J = 6.2 Hz,
3H, CCH3), 1.01 (d, J = 6.2 Hz, 3H, CCH3); 13C NMR (125 MHz, CDCl3):
d 170.6 (COCH3), 170.5 (2C, 2COCH3), 170.2 (COCH3), 155.3–114.9
(Ar-C), 155.5–114.8 (Ar-C), 106.5 (C-1C), 103.6 (C-1A), 101.9 (PhCH),
99.5 (3C, C-1D, C-1E, C-1F), 96.1 (C-1B), 81.3 (C-4D), 81.0 (C-3A), 80.6
(C-4E), 79.8 (C-3D), 79.2 (C-2B), 78.5 (C-4C), 78.4 (C-4B), 77.7 (C-3B),
77.5 (2C, C-2A, C-3E), 77.3 (C-2D), 76.1 (C-5A), 75.9 (PhCH2), 75.6
(PhCH2), 75.5 (C-2C), 75.4 (PhCH2), 75.0 (PhCH2), 74.9 (PhCH2),
74.1 (PhCH2),74.0 (C-4A), 73.9 (PhCH2), 73.3 (C-3C), 73.0 (PhCH2),
72.3 (C-2F), 72.2 (PhCH2), 71.1 (C-4F), 70.1 (C-2E), 69.6 (C-3F), 69.2
(C-6B), 68.9 (C-6A), 68.8 (C-6C), 68.7 (C-5B), 68.5 (C-5F), 68.0 (C-5E),
67.6 (C-5D), 67.4 (C-5C), 56.0 (OCH3), 21.4 (COCH3), 21.3 (COCH3),
21.2 (COCH3), 21.1 (COCH3), 18.0 (CCH3), 17.9 (CCH3), 17.6 (CCH3);
ESI-MS: m/z 2234.0 [M+Na]+; Anal. Calcd for C131H142O31
(2210.95): C, 71.11; H, 6.47. Found: C, 70.92; H, 6.73.
followed by TfOH (5 lL) were added to it. After stirring at the same
temperature for 30 min the reaction was quenched with Et3N
(50
l
L), filtered through a CeliteÒ bed and washed with CH2Cl2
(50 mL). The organic layer was washed with 5% Na2S2O3, satd NaH-
CO3, water in succession, dried (Na2SO4) and concentrated under
reduced pressure. The crude product was purified over SiO2 using
hexane–EtOAc (10:1) as an eluant to give pure 13 (1.8 g, 78%). Col-
ourless oil; ½a 2D5
¼ ꢀ6 (c 1.0, CHCl3); IR (neat): 3478, 3032, 2979,
ꢁ
2935, 1750, 1595, 1508, 1487, 1371, 1245, 1223, 1139, 1078,
1052, 983, 926, 830, 752, 699 cmꢀ1 1H NMR (500 MHz, CDCl3): d
;
7.35–7.25 (m, 19H, Ar-H), 6.89 (d, J = 9.1 Hz, 2H, Ar-H), 6.77 (d,
J = 9.1 Hz, 2H, Ar-H) 5.34 (br s, 1H, H-1D), 5.33–5.30 (m, 2H, H-2E,
H-2F), 5.24–5.21 (dd, J = 10.2, 3.3 Hz, 1H, H-3F), 5.05 (br s, 1H, H-
1E), 5.03 (t, J = 10.2 Hz each, H-4F), 4.97 (br s, 1H, H-1F), 4.85 (d,
J = 10.9 Hz, 1H, PhCH2), 4.78 (d, J = 10.9 Hz, 1H, PhCH2), 4.71–4.70
(m, 2H, PhCH2), 4.64 (d, J = 10.9 Hz, 1H, PhCH2), 4.60 (d,
J = 10.9 Hz, 1H, PhCH2), 4.20–4.18 (dd, J = 7.1, 3.4 Hz, 1H, H-3E),
4.07–4.03 (m, 1H, H-2D), 4.02–3.96 (m, 2H, H-3D, H-5D), 3.86–
3.81 (m, 2H, H-5E, H-5F), 3.75 (s, 3H, OCH3), 3.51–3.45 (m, 2H, H-
4D, H-4E), 2.21 (s, 3H, COCH3), 2.08 (s, 6H, 2COCH3), 1.99 (s, 3H,
COCH3), 1.31 (d, J = 6.2 Hz, 3H, CCH3), 1.24 (d, J = 6.2 Hz, 3H,
CCH3), 1.18 (d, J = 6.2 Hz, 3H, CCH3); 13C NMR (125 MHz, CDCl3):
d 171.4 (COCH3), 170.2 (COCH3), 170.1 (COCH3), 170.0 (COCH3),
155.3–114.9 (Ar-C), 99.6 (C-1E), 99.5 (C-1F), 97.9 (C-1D), 81.1 (C-
4D), 80.5 (C-4E), 79.7 (C-3D), 76.3 (C-3E), 76.1 (PhCH2), 75.8 (C-
2D), 75.7 (PhCH2), 72.6 (PhCH2), 72.2 (C-2E), 71.1 (C-4F), 70.1 (C-
2F), 69.5 (C-3F), 68.9 (2C, C-5E, C-5F), 67.7 (C-5D), 55.8 (OCH3),
21.4 (COCH3), 21.2 (COCH3), 21.1 (COCH3), 21.0 (COCH3), 18.5
(CCH3), 18.4 (CCH3), 17.6 (CCH3); ESI-MS: m/z 1023.4 [M+Na]+;
Anal. Calcd for C54H64O18 (1000.4): C, 64.79; H, 6.44. Found: C,
64.60; H, 6.27.
4.1.7. 4-Methoxyphenyl (2,3,4-tri-O-acetyl-
pyranosyl)-(1?3)-(2-O-acetyl-4-O-benzyl-aa
pyranosyl)-(1?2)-(3,4-di-O-benzyl- -rhamnopyranosyl)-
(1?3)-(4,6-O-benzylidene-b- -glucopyranosyl)-(1?4)-(2,3,6-
tri-O-benzyl- -galactopyranosyl)-(1?3)-2,4,6-tri-O-benzyl-b-
-galactopyranoside 15
To a solution of compound 13 (1.50 g, 1.50 mmol) in CH3CN–H2O
(15 mL; 4:1, v/v) was added ammonium cerium nitrate (CAN;
1.25 g, 2.28 mmol) and the reaction mixture was allowed to stir at
room temperature for 2 h. The reaction mixture was diluted with
CH2Cl2 (80 mL) and the organic layer was washed with satd NaHCO3
and water, dried (Na2SO4) and evaporated to dryness to give disac-
charide hemiacetal. To a solution of the hemiacetal in anhydrous
CH2Cl2 (15 mL) was added trichloroacetonitrile (1.2 mL, 12 mmol)
and the reaction mixture was cooled to ꢀ10 °C. To the cooled reac-
tion mixture was added DBU (0.1 mL, 0.65 mmol) and it was
allowed to stir at ꢀ10 °C for 1 h. The reaction mixture was evapo-
rated to dryness and the crude product was passed through a short
a
-
-
L
-rhamno-
-rhamno-
4.1.8. 4-Methoxyphenyl (2,3,4-tri-O-acetyl-
pyranosyl)-(1?3)-(2-O-acetyl-4-O-benzyl-
pyranosyl)-(1?2)-(3,4-di-O-benzyl- -rhamnopyranosyl)-
(1?3)-(2-O-acetyl-4,6-O-benzylidene-b- -mannopyranosyl)-
(1?4)-(2,3,6-tri-O-benzyl- -galactopyranosyl)-(1?3)-2,4,6-
tri-O-benzyl-b- -galactopyranoside 16
a
-
L
-rhamno
L
a-L-rhamno-
a-L
a-L
D
D
a
-D
a-D
D
D
To a solution of compound 15 (1.2 g, 0.54 mmol) in dry CH2Cl2
(10 mL) was added Dess–Martin periodinane (350 mg, 0.82 mmol)
and the reaction mixture was allowed to stir at room temperature
for 2 h. The reaction mixture was diluted with CH2Cl2 (50 mL) and
the organic layer was washed with 5% Na2S2O3 and water in suc-
cession. The organic layer was dried over Na2SO4, filtered and con-
centrated under reduced pressure to give the crude ketone as a
colourless oil, which was used in the next step without purifica-
tion. To a solution of the crude ketone in CH3OH (10 mL) was
slowly added NaBH4 (200 mg, 5.28 mmol) portionwise at 0 °C.
The reaction mixture was allowed to stir at room temperature
for 12 h and concentrated under reduced pressure. A solution of
the crude product in acetic anhydride–pyridine (5 mL; 1:1 v/v)
was allowed to stir at room temperature for 5 h and the solvents
were removed under reduced pressure. The crude mass was dis-
solved in CH2Cl2 (50 mL) and the organic layer was washed with
satd NaHCO3 and water, dried (Na2SO4) and concentrated under re-
duced pressure. The crude product was purified over SiO2 using
hexane–EtOAc (5:1) as an eluant to give pure 16 (900 mg, 74%).
pad of SiO2 to furnish (2,3,4-tri-O-acetyl-
(1?3)-(2-O-acetyl-4-O-benzyl- -rhamnopyranosyl)-(1?2)-3,4-
di-O-benzyl- -rhamnopyranosyl trichloroacetimidate (14; 1.2 g,
77%), which was used immediately for the next step. A solution of
compound (1.2 g, 0.95 mmol) and compound 14 (1.1 g,
1.06 mmol) in anhydrous CH2Cl2 (20 mL) was cooled to ꢀ20 °C. To
the cooled reaction mixture was added TMSOTf (30 L) and it was
a-L-rhamnopyranosyl)-
a
-L
a
-L
8
l
allowed to stir at ꢀ20 °C for 45 min. The reaction mixture was di-
luted with CH2Cl2 (50 mL) and the organic layer was washed with
satd NaHCO3 and water in succession, dried (Na2SO4) and evapo-
rated to dryness. The crude product was purified over SiO2 using
hexane–EtOAc (5:1) as an eluant to give pure 15 (1.6 g, 76%). Col-
Colourless oil; ½a D25
¼ ꢀ7:1 (c 1.0, CHCl3); IR (neat): 3450, 3032,
ꢁ
2925, 2855, 1748, 1508, 1455, 1371, 1228, 1139, 1092, 1045,
1029, 984, 750, 737, 698 cmꢀ1 1H NMR (500 MHz, CDCl3): d
;
7.23–7.08 (m, 50H, Ar-H), 6.86 (d, J = 9.1 Hz, 2H, Ar-H), 6.69 (d,
J = 9.1 Hz, 2H, Ar-H), 5.47 (d, J = 2.6 Hz, 1H, H-2C), 5.45 (s, 1H,
PhCH), 5.28–5.25 (m, 2H, H-2E, H-2F), 5.18–5.15 (dd, J = 10.1,
ourless oil; ½a 2D5
¼ ꢀ10 (c 1.0, CHCl3); IR (neat): 3435, 3031, 2929,
ꢁ

730
S. Ghosh, A. K. Misra / Tetrahedron: Asymmetry 21 (2010) 725–730
3.4 Hz, 1H, H-3F), 5.06 (d, J = 2.9 Hz, 1H, H-1B), 4.99 (br s, 1H, H-1F),
4.97 (br s, 1H, H-1E), 4.95–4.93 (m, 3H, PhCH2), 4.77 (br s, 1H, H-
1D), 4.74 (br s, 1H, H-1C), 4.73–4.71 (m, 3H, PhCH2), 4.66 (d,
J = 7.7 Hz, 1H, H-1A), 4.66–4.62 (m, 2H, PhCH2), 4.58–4.55 (m, 3H,
PhCH2), 4.52–4.43 (m, 3H, PhCH2), 4.36–4.20 (m, 6H, H-3C, H-3E,
PhCH2), 4.15–4.12 (dd, J = 9.6, 3.3 Hz, 1H, H-3D), 4.10–4.07 (m,
1H, H-2D), 3.99–3.91 (m, 3H, H-2A, H-4C, H-6aC), 3.84–3.80 (m,
3H, H-3B, H-4B, H-4F), 3.78–3.66 (m, 7H, H-4A, H-4E, H-5D, H-5F,
H-6abB, H-6bC), 3.68 (s, 3H, OCH3), 3.50–3.44 (m, 4H, H-5A, H-5B,
H-6abA), 3.40 (t, J = 9.6 Hz, 1H, H-4D), 3.36–3.27 (m, 3H, H-3A, H-
2B, H-5E), 3.12–3.08 (m, 1H, H-5C), 2.09 (s, 3H, COCH3), 2.02 (s,
3H, COCH3), 2.01 (s, 3H, COCH3), 1.98 (s, 3H, COCH3), 1.90 (s, 3H,
COCH3), 1.25 (d, J = 6.4 Hz, 3H, CCH3), 1.11 (d, J = 6.2 Hz, 3H,
CCH3), 1.06 (d, J = 6.2 Hz, 3H, CCH3); 13C NMR (125 MHz, CDCl3):
75.4 (C-4D), 73.3 (C-4E), 73.0 (C-5A), 72.2 (C-4F), 71.2 (C-5C), 71.1
(C-2F), 70.9 (C-3F), 70.8 (C-3E), 70.7 (C-2B), 70.4 (C-5D), 69.7 (2C,
C-5E, C-5F), 69.4 (C-6C), 69.2 (C-2A), 69.1 (C-5B), 67.9 (C-2D), 66.8
(C-3D), 66.2 (C-4C), 65.7 (C-2C), 62.6 (C-6B), 62.2 (C-6A), 55.2
(OCH3), 17.2 (CCH3), 17.1 (CCH3), 17.0 (CCH3); ESI-MS: 1071.4
[M+Na]+; Anal. Calcd for C43H68O29 (1048.38): C, 49.23; H, 6.53.
Found: C, 49.0; H, 6.80.
Acknowledgements
S.G. thanks UGC, New Delhi for providing a Senior Research Fel-
lowship. This work was partly supported by Ramanna Fellowship
(A.K.M.), Department of Science and Technology, New Delhi (SR/
S1/RFPC-06/2006).
d
170.6 (COCH3), 170.5 (2C, 2COCH3), 170.4 (COCH3), 170.2
(COCH3), 155.3–114.8 (Ar-C), 155.5–114.8 (Ar-C), 103.7 (C-1A),
101.6 (PhCH), 100.0 (C-1C), 99.5 (C-1F), 99.0 (C-1E), 95.9 (C-1D),
95.6 (C-1B), 81.3 (C-4D), 80.8 (C-3A), 80.0 (C-3D), 78.9 (C-4F), 78.4
(C-3B), 77.6 (C-2B), 76.9 (C-4C), 76.7 (C-4B), 76.0 (C-2A), 75.9 (PhCH),
75.6 (PhCH), 75.5 (C-3E), 75.3 (PhCH), 75.2 (PhCH), 74.9 (PhCH),
74.5 (C-2D), 74.1(C-5A), 73.8 (PhCH), 73.7 (PhCH), 72.9 (PhCH),
72.6 (C-2C), 72.3 (C-4A), 72.2 (PhCH), 71.9 (C-3C), 71.1 (C-2F), 70.1
(C-4F), 69.9 (C-6B), 69.6 (C-2E), 69.3 (C-6A), 68.9 (C-3F), 68.8 (C-
5B), 68.7 (C-6C), 68.4 (C-5F), 68.1 (C-5E), 67.6 (2C, C-5C, C-5D),
56.1 (OCH3), 21.4 (COCH3), 21.3 (COCH3), 21.2 (2C, 2COCH3), 21.1
(COCH3), 18.2 (CCH3), 18.1 (CCH3), 17.6 (CCH3); ESI-MS: m/z
2276.0 [M+Na]+; Anal. Calcd for C133H144O32 (2252.96): C, 70.85;
H, 6.44. Found: C, 70.64; H, 6.70.
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4.1.9. 4-Methoxyphenyl (
rhamnopyranosyl)-(1?2)-(
mannopyranosyl)-(1?4)-(
a
-
a
L
-rhamnopyranosyl)-(1?3)-(
-rhamnopyranosyl)-(1?3)-(b-
-galactopyranosyl)-(1?3)-b-
a-L-
-
D
L
D-
a
-
D-
galactopyranoside 1
A solution of compound 16 (800 mg, 0.35 mmol) in 0.1 M CH3O-
Na in CH3OH (25 mL) was allowed to stir at room temperature for
3 h. The reaction mixture was neutralized with Dowex 50W X8
(H+) resin, filtered and concentrated. To a solution of the deacety-
lated product in CH3OH (20 mL) was added 20% Pd(OH)2–C
(150 mg) and the reaction mixture was allowed to stir at room
temperature under a positive pressure of hydrogen for 24 h. The
reaction mixture was filtered through a CeliteÒ bed and then
washed with CH3OH–H2O (60 mL; 4:1 v/v). The combined filtrate
was evaporated under reduced pressure to furnish compound 1,
which was purified through a Sephadex LH-20 column using
CH3OH–H2O (5:1) as an eluant to give pure compound
1
(260 mg, 71%). White powder; ½a D25
¼ þ2:7 (c 1.0, CH3OH); IR
ꢁ
(KBr): 3405, 2921, 2850, 2718, 1596, 1509, 1354, 1224, 1129,
; d 6.96 (d,
1072, 985, 775 cmꢀ1 1H NMR (500 MHz, D2O):
J = 8.9 Hz, 2H, Ar-H), 6.86 (d, J = 8.9 Hz, 2H, Ar-H), 4.99 (br s, 1H,
H-1E), 4.97 (d, J = 3.7 Hz, 1H, H-1B), 4.95 (br s, 1H, H-1D), 4.85 (br
s, 1H, H-1F), 4.71 (d, J = 7.9 Hz, 1H, H-1A), 4.69 (br s, 1H, H-1C),
4.21–4.19 (m, 1H, H-2C), 4.17–4.16 (m, 1H, H-4B), 4.11 (br s, 1H,
H-4A), 4.03–3.98 (m, 2H, H-2B, H-2F), 3.91–3.87 (m, 3H, H-2D, H-
2E, H-3B), 3.86–3.72 (m, 5H, H-2A, H-2D, H-3D, H-6aB, H-6abC),
3.71–3.67 (m, 5H, H-3A, H-5A, H-6abA, H-6bB), 3.65 (s, 3H, OCH3),
3.64–3.55 (m, 5H, H-3C, H-3E, H-3F, H-4C, H-5D), 3.53–3.37 (m,
3H, H-4E, H-5E, H-5F), 3.34–3.29 (m, 2H, H-4D, H-4F), 3.26–3.21
(m, 2H, H-5B, H-5C), 1.20–1.14 (m, 9H, 3CCH3); 13C NMR
(125 MHz, CDCl3): d 155.6–114.5 (Ar-C), 103.1 (C-1F), 102.9 (C-
1E), 102.8 (C-1C), 101.5 (C-1A), 97.0 (C-1B), 95.4 (C-1D), 79.1 (C-
2E), 79.0 (C-3C), 78.4 (C-3B), 77.5 (C-3A), 77.1 (C-4A), 76.5 (C-4B),
20. Pearlman, W. M. Tetrahedron Lett. 1967, 8, 1663–1664.